Accelerator system for steam curing polymers



ACCELERATOR SYSTEM FOR STEAM CURING POLYMERS Wilbur Frank Fischer, Cranford, Robert Frederick Neu,

Westfield, and Robert L. Zapp, Florham Park, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware The present invention relates to curing hydrocarbon polymers in the presence of acombination of accelerators. More specifically, it relates to curing isoolefinmultiolefin polymers in an atmosphere containing moisture by using a combination of dithiocarbamates and thiazoles. Moreover, it concerns the improved vulcanizates obtained by this process.

Earlier natural rubber was cured in the presence of steam by using sulfur as the curing agent. More recently it has been noted that both natural and synthetic rubbers can be more rapidly and thoroughly cured by employing sulfur and accelerators. of accelerators are the dithiocarbamates, especially those types containing high hydrocarbon substituents such as tellurium ethyl benzyl dithiocarbamate. These substances are especially important in the case of butyl rubber which would otherwise have a surface with a low state of cure. The higher substituted dithiocarbamates are more efiective because they are less water sensitive than say the diethyl derivative. are costly it is generally advisable to use as little as possible of these higher molecular weight derivatives in compounding the rubber.

It has now been found that certain other accelerators,

when combined with the higher substituent dithiocar Unit S a s en 1 "1 One of the most effective classes However, because these compounds especially effective in butyl rubber.. The high unsaturahas about 4-7 carbon atomsQand about 10-05% by weight of a conjugated multiolefin having about 4-l4 carbon atoms. The term butyl rubber is described in an article by R. M. Thomas et al, in Industrial Engineering and Chemistry, vol. 32, pages 1283 et seq., October In preparing butyl rubber polymer, the isoolefin and mutiolefin are mixed in the ratio of a major proportion of the multiolefin, the preferred range being about 70 to' 99.5, preferably 85 to 99.5 parts by weight of the isoolefin to about to 0.5, preferably 0.5 to 15 parts by weight of the multiolefin. High purity is desirable in both materials, it being preferable'to use an isoolefin of at least made from multiolefins of a lower purity. I

In general, the rubber comprises the reactionproduct 98% purity, although satisfactory copolymers may be Of ac, to'C'} isoolefin, such asisobutylenebr z-niethyl lgroup containing 4 to 10 carbonatomsy aryl, cycloparaflinic or alkar'yl group containing;

0 .The dithiocarbamate accelerators coming within 2,917,345; Patented, Man. 28, 1951.

2 butene, with a C to C conjugated diolefin, such as isoprene, butadieneor piperylene. The reaction product; product of isobutylene and isoprene is preferred. For; instance, 97 to 97.5% by weight of isobutylene is reacted v with 2.5 to 3.4% by weight of isoprene I I The mixture of-monomers is cooled to a temperature within the range between about 0 and 200 C., preferably between about 40 and -l60" C. It is especially preferred that the reaction temperature be between 60 C. and -130 C. The materials may be cooled by the use of a refrigerating jacket, whichsurrounds the mixing tank, for instance using liquefied ethylene as cooling liquid. Alternatively, the mixture 'may be cooled by means of an internal refrigerant. In this case, it is mixed directly with the startingmaterials. Refrigerants which have been found to be satisfactory for internal use are liquid propane, solid carbon dioxide, liquid ethane, liquid ethylene,etc. The cold mixture ispolymerized by the addition ofa- Friedel-Crafts catalyst, preferably an aluminum ,halidm catalyst in a liquid or dissolved form, with vigorous agita tion. The amount of catalyst employed is generally about; 0.15% to about 1.0% by weight of the mixed olefin s. The liquid catalyst may be sprayed on to the surfaceof the rapidly stirred mixture, or it may be introduced in; the form of a pressured stream. a a

g r The polymerization reaction proceeds rapidly. 'Ihet polymerprecipitates out of solution in the form, of pa slurry of flocculentwhite solid. When the polymerization has reached the desired stage, the material is conveniently recovered by charging the whole mixture into warm water which may contain alcohol, ether, aldehyde or organic acid to inactivate the catalyst. The polymer is then recovered from the water suspension in any con- 45,000 and 60,000. The material has a Wijs iodine num ber between about 0.5 and 50, generally between about I and 15. The preparation of the above rubbery butyl copolymer is described in US. Patent No. 2,356,1 28'10.- which reference may be had'for further details, 7 According to the present invention butyl rubber'is curedin open steam at a temperature between about 200 C-i I I I and C. for from about 20 secondsup' to 3Ihours in the presence of sulfur or a sulfur-containing curing agenfl a thiazole and a dithiocarbamate in'which at leastione ofvthe two hydrocarbon groups that are attac'hed't'o it gong; tains 4 to 10 or 14icarbon'at'oms, while the other hy-j drocarbon group may contain from 2 tolOcarbo'n atoms: A. preferred embodiment of the invention is'iwhere'iat least one or both of the hydrocarbon groups-iii fthefdi thiocarbamate is'cyclic and contains 6 to 10 car'boriat'oms, for instance, aryl, alkaryl, cyclo'parafiinicfalkyl, ary rid diaryl derivatives. It has been 'notedthat'fthesell accelerators in combinationw'ith the'thiazoles produce vulcanizates that are exceptionally resistantktojozo oxidation.

purview of the invention have the followingl ge formula:'' I I II I a NC Metal 11 S- -x i' L, or a wherein R' is an-a'lkyL. arylpc'ycloparaiiin carbon atoms; the metal is tellurium, copper, zinc, lead,

iron, calcium, strontium, potassium or sodium; x is the valence of the metal and isgenerally between 1 and 4, although it is usually better to use metals having a valence of 2 to 4. Group I-B and VI-A metals in the periodic table, especially tellurium and copper, are preferred because they bring about a faster cure. The preferred bydrocarbon groups are butyl, pentyl, hexyl, octyl, nonyl, decyl, cyclohexyl, benzyl and combinations thereof with themselves or lower hydrocarbon groups such as ethyl and propyl.

The coaccelerator may be a thiazole or preferably an aryl thiazole having a sulfur attached to the thiazole ring or nucleus. It may have the following general formula:

The ozone resistant butyl rubbers may be blended and cured with a higher unsaturation rubber using special curing systems such as an amine, e.g. diortho tolyl guanidine, and sulfur. For instance about 1 to 50 parts of GR-S or natural rubber may be blended with 100 parts of butyl rubber and 1 to 4 parts of the accelerators. Other conventional compounding materials may also be used, such as fillers, oil extenders,- softeners, stabilizers, etc.

The following examples are given to more fully illustrate the various embodiments of the present invention. All recipes are in parts by weight.

EXAMPLE 1 Isobutylene-isoprene butyl rubber (formerly known as GR-l-l8), was compounded in a Banbury according to the following formula:

Ingredients: Parts Butyl 100 HMF black 30 SRF black 80 Zinc oxide 5 Naphthenic oil (Nection 60) 10 The sulfur (1.5 part) and accelerators were added on a cold laboratory mill in the conventional manner. An extruded strip of each sample was steam cured for 30 minutes at 320 F. The vulcanizates were cut into dumbbells 0.075 inch thick (ASTM-D-4l2-51T) having /2 inch wide shoulders, stretched 50% and allowed to stand for 30 minutes before being put in an atmosphere containing 50 pphm of ozone in air at 38 C.

Ozone Observations Water Run Accelerators(s) phrJ Absorp tlon 3 hrs. 19 hrs. 27 hrs. Percent Tellurium dlethyl dithiocarbamate- 2 0+ 2 2 1. 95 Tellurium ethyl benzyl dithio- 2. 8 0 0+ 1 1.60 Tessa- 5 1. Benzothiazyl disulfide 1. s 0 43 lli ti ttghlazyljdisulfide 2. g

l. Mercaptobenzothlazole 1. 3 i 0 0+ 1 61 lvlercaptobenzothlazole 2. 6 'PEBD 1. 5 07 Zinc benzothiazyl sulfide 1 3 0 0+ 0+ 1. 45 3% Tetramethyl thiuram disulfide- Phr.=parts per hundred parts of (butyl) rubber. =TEBD=Tel1urium ethyl benzyl dithlocarbamate.

weight of the sulfur-liberating compounds and a minor amount of the dithiocarbamate and thiazole accelerators, say about 0.5 to 10 parts by weight, in a ratio of 1:1 to 1:3 parts by weight to one another are mixed with 100 parts by weight of butyl rubber and cured in the presence of open steam for from about 15 to 100 minutes. For most purposes about 1 to 5 parts by weight of the combined accelerators are sufficient to improve the vulcanizate. It is generally desirable to also have about 3 to 10 parts by weight of a divalent metal oxide, such as zinc oxide, present during the curing operation. I

The compounded butyl rubber is usually extruded at a temperature between 100 and 200 C. and cured in position. That is to say, a wire coated with a film, say, about ,6 to /2 inch thick may be passed through a steam chamber at such a rate that the compounded butyl rubber film is cured by the time it leaves the chamber. A second method consists of taking the extruded or preformed articles and statically vulcanizing the article in a steam autoclave. One of the advantages of the "present invention is that the rubber is thoroughly cured and has little or no surface tack such as is frequently connected with this type of cure. It has also been noted that the accelerators of the present invention form a more homogeneous mixture with the butyl rubber and it is believed The percent water absorption was determined at C. based on the gain in weight of a strip (0.070" x 0.75" x 4f). Low water absorption values are desired since they indicate decreased water sensitivity of the curatives during curing, for example, TEBD and benzothiazyl disulfide, which results in better surface cure and superior ozone resistance. r

The ozone ratings may be defined as follows:

0=no cracks visible under 7 X magnification 0+=slight cracks visible under 7 X magnification =cracks visible to naked eye 2=large cracks each other. The following compounding formulation was used.

combination of accelerators consisting essentially o f tel lurium ethyl benzyl dithiocarbamate and benzothiazyl disulfide, said combination of accelerators containing bbigi rubber 1 about 0.3 P ts by weight of benzothiazyl disulfide Carbon black (Philbla k A) 30 5 P P y Weight f t llurium ethyl benzyl dithiocan Sterling R (SRF carbon black) so v Zi Oxide 5 2. A composition according to clalm 1 comprising 0.6 S i ulfu L5 to 1.2 parts by weight of benzothiazyl d1s ulfide per part Plasticizer oil (Necton 60) y Welght 0f Q i m ethyl benzyl dithiocarbamate. Accelerators (2) 10 3. A composltion'of matter comprising 100 parts by weight of a butyl rubber copolymer of 85 to 99.5 wt. percent of a C to C isoolefin and 0.5 to wt. percent of a C to C multiolefin, cured with sulfur in the presence of about 0.5 to 10 parts by weight of an acceleraon physical properties and ozone resistance are shown 15 tor combination, said accelerator combination consistin the following table. ing of telluriumethyl benzyl dithiocarbamate and benzo-.

Efiect of ethyl benzyl Tellurac -Altax concentration on properties of butyl rubber vulcanizates Having an unsaturution of about 0.6 to 1.0 mole percent, and a Mooney viscosity of about 38 to 47.

As indicated below.

The amounts of accelerators used and the data obtained a Tellurium ethyl benzyl dithiocarbarnate. Altax=benzothlazyl dlsulfide.

b 50 phm. ozone, 50% dumbbell extension.

Physical properties and particularly ozone data obtained on steam cured vulcanizates show a distinct advantage for a combination of about 1.5 phr. of EBT and 1.3 phr. of Altax as compared to the performance level of 2.8 phr. of either accelerator alone. Straight Altax is very difiicient on original physicals and ozone resistance while EBT alone is slightly poorer on physicals and definitely poorer on ozone resistance. From a practical use viewpoint, the combination of accelerator shows an advantage is cost compounding and should considerably improve the useful life of the butyl rubber vulcanizate.

Thus, generally, according to the present invention it is desirable to use about 0.3 to 2.5 parts of the thiazole per part of the dithiocarbamate. More specifically, for instance, it is desirable to use about 0.4 to 1.5, preferably 0.6 to 1.2, and best about 0.8 to 0.9, parts of Altax per part of EBT.

Resort may be had to various modifications and variations of the present invention without departing from the spirit of the discovery or the scope of the appended claims.

What is claimed is:

1. A composition of matter having good ozone resistance comprising, 100 parts by weight of a butyl rubber copolymer of 85 to 99.5 wt. percent of a C to 0, isoolefin and 0.5 to 15 wt. percent of a C to C multiolefin, cured with sulfur in the presence of about 0.5 to 10 parts by weight of a combination of accelerators, said thiazyl disulfide, and wherein said accelerator combination contains 0.3 to 2.5 parts by weight of benzothiazyl disulfide per part by weight of tellurium ethyl benzyldi thiocarbamate.

4. A process for curing a butyl rubber copolymer of to 99.5 wt. percent of a C to C isoolefin and 15 to A I 0.5 wt. percent of a C to C multiolefin, which com-- 1 I prises, mixing said butyl rubber copolymer with a curing agent, and 0.5 to 10 wt. percent based on copolymer ofa combination of accelerators, said combination of ac g celerators consisting essentially of tellurium ethyl benzyl dithiocarbamate and benzothiazyl disulfide, about 0.3 to r 2.5 parts by weight of benzothiazyl disulfide being em? ployed per part by weight of tellurium ethyl benzyl d ithiocarbamate, and curing said mixture with steam'at" to 200 C.

OTHER REFERENCES Vanderbilt Rubber Handbook, 1948, R. ryaidei-bitg 00., page 80 and page 50, paragraph 2. 71 I 

1. A COMPOSITION OF MATTER HAVING GOOD OZONE RESISTANCE COMPRISING, 100 PARTS BY WEIGHT OF A BUTYL RUBBER COPOLYMER OF 85 TO 99.5 WT PERCENT OF A C4 TO C7 ISOOLEFIN AND 0.5 TO 15 WT. PERCENT OF A C4 TO C10 MULTIOLEFIN, CURED WITH SULFUR IN THE PRESENCE OF ABOUT 0.5 TO 10 PARTS BY WEIGHT OF A COMBINATION OF ACCELERATORS, SAID COMBINATION OF ACCELERATORS CONSISTING ESSENTIALLY OF TELLURIUM ETHYL BENZYL DITHIOCARBAMATE AND BENZOTHIAZYL DISULFIDE, SAID COMBINATION OF ACCELERATORS CONTAINING ABOUT 0.3 TO 2.5 PARTS BY WEIGHT OF BENZOTHIAZYL DISULFIDE PER PART BY WEIGHT OF TELLURIUM ETHYL BENZYL DITHIOCARBAMATE. 